Abstract A long-time drawback of dental composites is that they accumulate more biofilms and plaques than amalgam and glass ionomer restorative materials. It would be highly desirable to develop a new composite with reduced biofilm growth, while avoiding the non-esthetics of amalgam and low strength of glass ionomer. The objectives of this study were to: 1 develop a protein-repellent composite with reduced biofilms matching amalgam and glass ionomer for the first time; and 2 investigate their protein adsorption, biofilms, and mechanical properties. Five materials were tested: A new composite containing 3% of protein-repellent 2-methacryloyloxyethyl phosphorylcholine MPC; the composite with 0% MPC as control; commercial composite control; dental amalgam; resin-modified glass ionomer RMGI. A dental plaque microcosm biofilm model with human saliva as inoculum was used to investigate metabolic activity, colony-forming units CFU, and lactic acid production. Composite with 3% MPC had flexural strength similar to those with 0% MPC and commercial composite control p > 0.1, and much greater than RMGI p < 0.05. Composite with 3% MPC had protein adsorption that was only 1-10 that of control composites p < 0.05. Composite with 3% MPC had biofilm CFU and lactic acid much lower than control composites p < 0.05. Biofilm growth, metabolic activity and lactic acid on the new composite with 3% MPC were reduced to the low level of amalgam and RMGI p > 0.1. In conclusion, a new protein-repellent dental resin composite reduced oral biofilm growth and acid production to the low levels of non-esthetic amalgam and RMGI for the first time. The long-held conclusion that dental composites accumulate more biofilms than amalgam and glass ionomer is no longer true. The novel composite is promising to finally overcome the major biofilm-accumulation drawback of dental composites in order to reduce biofilm acids and secondary caries. View Full-Text